1. Field of the Invention
The present invention relates to a rotary apparatus and a laser beam printer having a rotary apparatus, and more particularly to a rotary apparatus for rotating a polygon mirror or the like, and a laser beam printer having such a rotary apparatus.
2. Description of the Related Art
Recently, a rotary apparatus is requested to conduct high-speed or high-accuracy rotation. For example, a laser beam printer requires a high-accuracy rotary apparatus for a polygon mirror. Such a rotary apparatus must be designed so as to prevent the polygon mirror from dropping off during a rotating process.
For example, JP-A-4-107313 discloses a rotary bearing which has a hydrodynamic bearing, and in which a concave portion is disposed in a rotation shaft, a projecting member that is to be fitted into the concave portion in a contactless manner is disposed on a sleeve, and the projecting member has a shape that, when the rotation shaft is fitted into the sleeve, is easily deformed, and that is caught in the pulling out direction, thereby preventing the rotation shaft from dropping off.
In this structure, a rotary member attached to the rotation shaft is prevented from being lifted up more than needed from a fixing member, or being pulled out thereof.
In the apparatus of JP-A-4-107313, however, the projecting member must have an elastic shape, and hence must be thinned, so that the durability is reduced. When the projecting member is made of a material different from that of the sleeve or formed as a part separate from the sleeve, the number of production steps and the production cost are increased. Moreover, the rotation shaft is hardly pulled out of the sleeve, and hence the rotation shaft and the sleeve must be replaced together with new ones in a repairing process or the like.